In motorcycles having a fuel injection system, a system is provided for automatically stopping the engine by stopping the fuel pump when the vehicle has tumbled. For example, in a motorcycle described in Japanese Utility Model Publication No. Sho 60-4857, a spherical magnet is rollably placed inside a U-shaped groove formed in a non-magnetic case. The rolling of the spherical magnet in response to an inclination of the vehicle body is sensed by a reed switch, whereby the tumbling of the vehicle body is detected, and the engine is stopped.
Known tumble detecting sensors for a motorcycle detect when the vehicle body is inclined to either the left or right side by an amount of not less than a predetermined value. In response to this detection, the engine is stopped. In cases of motorcycles where the vehicle body may be expected to tumble to the left or right side, such a sensor detects the tumble of the vehicle body, and the engine can be stopped. In the case of a saddle ride type all-terrain vehicle (hereinafter referred to as “ATV”), on the other hand, the determination of tumble (or roll over) should be taken into account not only in the left-right direction but also in the front-rear direction, for example, when the vehicle is ascending or descending a steep slope or in like situations.